Storage tube with improved flood gun



Jan. 10, 1961 c. D. BEINTEMA 2,967,971

STORAGE TUBE WITH IMPROVED FLOOD GUN Filed Aug. 14, 1957 3 Sheets-Sheet 1 Chester D. Bein'remu,

INVENTOR.

AGENT 1 19 c. D. BEINTEMA 2,967,971

STORAGE TUBE WITH IMPROVED FLOOD GUN Filed Aug. 14, 1957 3 Sheets-Sheet 2 Chester D. Beintemu,

INVENTOH.

PM 0. at

AGE/VT.

Jan. 10, 1961 c. D. BEINTEMA STORAGE TUBE WITH IMPROVED FLOOD GUN 3 Sheets-Sheet 3 Filed Aug. 14, 1957 Chester D Beimem INVENTOR.

PM k;

United States Patent O i STORAGE TUBE WITH IMPROVED FLOOD GUN Chester D. Beinterna, Santa Monica, Calif., assignor t Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Aug. 14, 1957, Ser. No. 678,079

2 Claims. (Cl. 315-12) This invention relates to direct-vievw'ng storage tubes, and more particularly to an indicator tube of the cathode-ray type incorporating a ring-type flood gun and associated apparatus for collimating the flood electrons.

The direct-viewing storage tube of the present invention is of the same type as disclosed in copending application for patent Serial No. 536,875, entitled Multicolor Storage Tube, filed by Sidney T. Smith, on September 27, 1955, now U.S. Patent 2,910,617, and assigned to the same assignee as the present application. More particularly, the direct-viewing storage tube of the present invention comprises three electron guns for producing, respectively, three electron beams which are scanned over a storage screen disposed adjacent to and coextensive with a three-color phosphor dot viewing screen. The storage screen is characterized by the fact that it has a single aperture disposed in alignment with each phosphor dot of the viewing screen. A shadow mask is interposed between the electron guns and the storage screen. The shadow mask is disposed adjacent to and coextensive with the storage screen and has one opening for each set of three apertures of the storage screen which are in alignment with three adjacent different colored phosphor dots on the viewing screen. The placement of the apertures in the storage screen relative to the openings in the shadow mask is such that each electron beam, upon penetrating through an opening in the shadow mask, is incident on the storage surface surrounding only the aperture in the storage screen in alignment with its associated color of phosphor dot on the viewing screen. A color presentation is then produced by directing flood electrons through the shadow mask and thence through the apertures in the storage screen in proportion to the charge on the surrounding storage surface to the corresponding phosphor dots on the viewing screen. In order to maintain color purity and uniformity of illumination, it is necessary that the flood electrons be directed towards the shadow mask at substantially normal incidence and that the entire flood beam be of uniform intensity. In accordance with the present invention, a flood beam of the aforementioned type is produced by means of a flood gun incorporating a double-ring cathode disposed about the mean paths of the electron beams, which gun operates in conjunction with an annular funnel-shaped converging electrode to properly collimate the flood electrons.

It is therefore an object of the invention to provide an improved direct-viewing half-tone storage tube.

Another object of the invention is to provide a directviewing storage tube incorporating an improved flood gun and flood beam collimating apparatus.

A further object of the invention is to provide an improved flood gun adapted for use in a direct-viewing halfttone storage tube, said flood gun having a double-ring directly heated cathode connected at numerous points in a manner to minimize the voltage drop therearound.

The above-mentioned and other features and objects 2,967,971 Patented Jan. 10, 1961 of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a longitudinal sectional view of a direct-viewing storage tube embodying the present invention;

-Fig. 2 is a greatly enlarged view of a portion of'the viewing screen in the device of Fig. 1;

Figs. 3 and 4 are greatly enlarged plan and cross-sectional views, respectively, of the storage screen in the device of Fig. 1;

Figs. 5 and 6 are greatly enlarged plan and cross-sectional views, respectively, of the: shadow mask in the device of Fig. 1;

Fig. 7 is a greatly enlarged plan view showing the manner in which the phosphor dots of the viewing screen, the apertures in the storage screen, and the openings in the shadow mask are aligned at a central portion of the viewing screen in the device of Fig. 1;

Fig. 8 is a schematic view in perspective illustrating the manner in which the three electron beams of the electron guns in the device of Fig. 1 pass through a given opening in the shadow mask and .impinge on the storage surface surrounding selected apertures in the storage surface; and

Figs. 9 and 10 are perspective and plan views, respectively, of the flood gun in the device of Fig. 1.

Reference will be made first to Fig. 1 for a general description of an illustrative embodiment of the directviewing storage device of the present invention. The de vice comprises an evacuated bulbous envelope 10 including an annular metal portion 11, a glass-viewing plate 12 and a neck portion 13 at the opposite extremity from the viewing plate 12. For the purpose of explanation, it will be assumed that a presentation having three primary colors is to be produced. Accordingly, the neck portion 13 of the envelope 10 is adapted to house electron guns 14, 16 and 18. These electron guns are symmetrically disposed about the longitudinal axis through the neck portion 13 and are equal in number to the aforementioned number of: primary colors. The three electron guns 14, 16 and 18 are conventional and produce three electron beams which are represented schematically in the right portion of the envelope 10, as viewed in the drawing, with their angular relationships greatly exaggerated, for purposes of illustration, by the dashed lines 20, 22 and 24, respectively. Each of the electron guns 14, 16, 18 has impressed thereon a video color signal provided by a video source 26 in a manner to intensity modulate the electron beams 20, 22 and 24, respectively.

Adjacent the viewing plate 12 of the envelope 10 there is disposed, in the order named, a viewing screen 28 in actual contact therewith, a storage screen 30, a shadow mask 32 and a shield grid 33. In addition, a magnetic convergence coil 34 and magnetic electron beam deflecting yokes 36, 38 are disposed about the outside of the neck portion 13 of envelope 10 for con-' verging the electron beams together in the plane of the shadow mask 32 and for simultaneously directing the electron beams toward selected elemental areas of the storage screen 30, respectively. It is realized, of course, that the angles between the beams 20, 22, 24 and the spacing between the shadow mask 32 and the storage screen 30 as compared with the length of the tube are exaggerated for better illustration of the operation of the tube.

More particularly, as indicated in Fig. 1, the viewing screen 28 is disposed directly on the inner surface of the viewing plate 12 of evacuated envelope 10. The viewing screen 28 comprises a transparent conductive coating 50 on top of which is disposed a phosphor dot viewing -to the phosphor dots on the viewing screen 28.

screen 52, as shown in Fig. 2. An aluminized layer over the phosphor dots could be used in lieu of the conductive coating. In the event that it is desired to reproduce the true colors of a picture, the phosphor dots of the viewing screen 28 are composed of three primary colors such as, for example, red, blue and green. These phosphor dots may have a diameter of the order of 0.0136 inch and are arranged so that the perimeter of a dot of any one color just touches the perimeter of dots of the remaining two color dots disposed alternately thereabout as illustrated in the figure. Thus, as can be seen in this figure, any group of three dots in mutual contact with each other includes one each of the primary color dots.

Referring to Figs. 1, 3 and 4, the storage screen 30 is disposed adjacent to and coextensive with the viewing screen 28 and may comprise, for example, a thin sheet 54 of metal of the order of 0.004 inch thick which has apertures 56 of a diameter of the order of 0.004 inch in alignment with each phosphor dot of the viewing screen 28. It has been found that an alloy of 95% cop per and 5% nickel is a suitable metal out of which to fabricate the sheet 54 of the storage screen. A thin layer 58 of dielectric material having secondary electron emis sion characteristics such as, for example, magnesium fluoride is evaporated on the side of the metallic sheet 54 facing the electron guns 14, 16 and 18. In the event magnesium fluoride is used, this layer 58 is of a uniform thickness of the order of two microns.

When evaporating the layer 58 of dielectric material on the one side of the metallic sheet 54, it is essential that no particles of dielectric material be deposited within the apertures 56 in an unsymmetrical way. The reason for this is that, in order to maintain color purity, it is necessary that no transverse velocity be imparted to the flood electrons in traversing through the apertures 56 In operation, any particles of dielectric deposited within the apertures 56 may accumulate erroneous charges from the viewing screen 28 or from the electron beams 20, 22, 24 and thus impart suflicient transverse components of velocity to the flood electrons to cause them to impinge on an adjacent phosphor dot. In addition it may be desirable to leave a small symmetrical portion of the metallic plate 54 about each of the apertures 56 exposed so as to increase the range potentials over which half-tone signals may be stored. The manner in which a screen of this type may be fabricated is taught in a copending application for patent, Serial No. 519,384, filed June 30, 1955, now US. Patent 2,858,463, entitled Storage Screen for Direct-Viewing Storage Tube, by Sidney T. Smith and Nobuo I. Koda and assigned to the same assignee as is the present application. As taught in the above application for patent, the metallic plate 54 is coated with a layer of photoresist, one side of the coated plate 54 exposed to light to harden the photoresist, and the unexposed portions of the layer of photoresist dissolved away. A layer of magnesium fluoride may then be evaporated on the exposed portions of the metallic plate 54. The hardened portions of the layer of photoresist may then be burned olf leaving a layer of magnesium fluoride on only one side of the metallic sheet 54. In the event that it is desired to have a narrow border 57 of exposed metal about the outer periphery of each aperture 56, additional metal may be electroplated within each of the apertures until borders of the desired width are produced. When metal is electroplated within apertures 56 in this manner, their initial diameter should make an allowance for the amount by which it will decrease due to the electroplating operation.

The shadow mask 32 is disposed adjacent to and coextensive with the storage screen 30 on the side thereof facing the electron guns 14, 16, 18. As shown in Figs. 5 and 6, the shadow mask 32 has one opening 60 for each set of three of the apertures 56 in the storage screen 30. When fabricating shadow mask 32, it is preferable to use the same material chosen for the metallic plate 54 of the storage screen 30. Thus, in the present case, a metal sheet 61 of the order of 0.004" thick composed of an alloy 95% copper and 5% nickel is a suitable material out of which to fabricate the shadow mask 32. In the center portion of the mask 32 and the screens 28, 30, the openings 60 of the shadow mask 32, the apertures 56 of the storage screen 30, and the phosphor dots 52 of the viewing screen 28 are aligned in the manner shown in Fig. 7. In this figure the phosphor dots 52, apertures 56, and the openings 60 are all projected into a single plane and an opening 60 is represented by a shaded circle. Each of the apertures 56 is centrally located over a different color phosphor dot. The opening 60, on the other hand, is disposed so that its outer periphery is equidistant from the center of each of the apertures 56. In the regions nearer the outer periphery of the mask 32, on the other hand, allowance must, of course, be made for parallax of the electron beams. Thus, it is necessary to align the openings 60 of the shadow mask 32 with both the phosphor dots 52 of the viewing screen 28 and the apertures 56 of the storage screen 30. The spacing between the shadow mask 32 and the storage screen 30 is determined by the spacing between the apertures 56, the distance from the shadow mask 32 to the centers of deflection of the electron beams 20, 22, 24 and the distance separating the centerss of deflection of the elec tron beams.

Disposed about the paths of the electron beams 20, 22 and 24 produced by electron guns 14, 16 and 18, respectively, is a ring-type flood gun 70 which is con structed in accordance with the present invention, as will be hereinafter described. An equipotential region is provided intermediate the electron guns 14, 16, 18 and the flood gun 70 by means of a conductive coating 72 disposed therebetween on the inner surface of the neck portion 13 of envelope 1%). Apparatus adapted to collimate the flow of electrons includes a collimator electrode 74 disposed adjacent to the shield grid 33 and coextensive with the image area of the tube. Collimator electrode 74 is a funnel shaped electrode constituting a first annular portion 75 of a diameter corresponding to the image area adjacent the shield grid 33, a second annular portion 76 of a diameter somewhat less than the inner diameter of envelope 10 nearest the flood gun 70, and a conical section 77 adapted to connect the first and second annular portions 75, '76. As shown in the draw ing, the diameter of the second annular portion 76 will be of the order of 25% larger than the diameter of the first annular portion 76. Also included in the apparatus adapted to collimate the flow of electrons is a conductive coating 78 disposed about the inner surface of envelope 10 and extending from the flood gun 70 to the nearest edge of the collimator electrode 74.

In order to more adequately describe the flood gun 70 and the electrical connections thereto, reference is made to Figs. 9 and 10. Thus, flood gun 70 comprises a reflector 80 constituting annular portions 81 and 82 together with conical portion 83 which are fastened to a common side of a circular disc 84 to form two circular channels that are adapted to accommodate inner and outer circular cathodes 86, 88, respectively. In that a charge pattern on the storage screen 30 of the present device functions in a manner to control the flow of flood electrons to the viewing screen 28, the potential of the source, i.e., cathodes 86, 88, must be maintained as uniform as possible. This would normally dictate the use of an indirectly heated cathode where the entire electron emitting surface is always at a substantially constant potential. In the present situation, however, an indirectly heated cathode capable of emitting the requisite flood beam current would also liberate an excessive amount of heat. Thus, in accordance with the present invention, cathodes 86, 88 are provided by directly heated circular tungsten filaments which liberate substantially less heat. 88 are supported and connections made thereto at, for example, thirty-eight equally spaced intervals by means of an equivalent number of support and connecting pins 90 which extend through and are insulated from the circular disc 84. Further, alternate connecting pins 90 of both filaments 86 and 88 are connected to a common bus 91 which, in turn, is connected to ground and to the center tap of the secondary winding of a filament transformer 92. The remaining support and connecting pins 90 associated with filament 86 are connected to a bus 93 and the remaining support and connecting pins 90 associated with filament 88 are connected to a bus 94. Buses 93 and 94 are, in turn, connected to the output terminals of the secondary winding of filament transformer 92 which winding provides an excitation of the order of 2 volts R.M.S. (root-mean-square). Thus, the maximum potential deviations are of the order of 1.4 volts with respect to ground and occur at points which are spread uniformly around the filaments 86, 88.

During the operation of the device, the conductive coating 72, the reflector 80 of flood gun 70, conductive coating 78 and collimator electrode 74 are maintained at +30 volts, zero volts, +50 volts and +60 volts, respectively, with respect to ground. Thus, conductive coating 78 and collimator electrode 74 provide electrostatic fields which form a weak electrostatic lens adapted to collimate the flow of flood electrons. Also, the cathodes of the electron guns 14, 16, 18 are maintained at a potential of the order of -6000 volts with respect to the mean potential of the cathodes 86, 88 of the flood gun 70, which is in the instant case, maintained at ground potential. Under these circumstances, the shield grid 33 is maintained at +100 volts, the shadow mask 32 is maintained at +1000 volts, the metal sheet 54 of the storage screen 32 at +8 volts, and the transparent conductive coating 50 of the viewing screen 28 at 6000 volts positive with respect to ground. The electron beams 20, 22 and 24 are first directed along the neck portion 13 parallel with each other until they arrive at the centers of deflection 62, 63, 64, respectively, of the yokes 36, 38, as indicated in Fig. 8. Simultaneously with being scanned over the shadow mask shown in Fig. 8, the electron beams 20, 22, 24 (only portions of which are shown) are converged towards a common point in the plane of the mask 32 in the usual manner. The electron beams pass through the openings 60 of the shadow mask 32 and impinge on the storage surface surrounding the apertures 56 directly opposite phosphor dots of the viewing screen 28 of a color corresponding with the signal employed to modulate the electron guns 14, 16, 18. In that the electron beams 20, 22, 24 would have to traverse both the shadow mask 32 and the storage screen 30 to impinge on the viewing screen 28, their etficiency to produce light upon reaching screen 28 is less than of what it would be if the beams 20, 22, 24 were unintercepted. Simultaneously, with the beams 20, 22, 24 charging the storage surface surrounding the apertures 56 of storage screen 30, flood electrons emanating from the directly heated ring filaments 86, 88 of the flood gun 70 are directed in a diverging beam towards the shield grid 33 as a result of the electrostatic fields established by the reflector 80 In the instant case, filaments 86,

of flood gun and conductive coating 78. Also, the dual source of the flood electrons (i.e., filaments 86, 88) greatly improves the extent to which the flood electrons penetrate through the shadow mask 32 in a manner that will retain color purity in the presentation. More particularly, each opening 60 in the shadow mask 32 acts as a diverging lens to the flood electrons due to the negative potential gradient from the mask 32 to the storage screen 30. This lens calculates to be weak and tends to be beneficial in that it improves the uniformity of the flood electrons and avoids shadowing of flood electrons by the shadow mask 32. In order for this lens to operate properly, however, it is necessary for the flow of flood electrons to be substantially normal to the plane of shadow mask 32. This lens effect is, of course, negligible for the high-velocity beams 20, 22 and 24. The flood electrons which approach the storage surface may be reflected or captured by one of the converging lenses produced in the vicinity of the apertures 56 of the storage screen 30. Flood electrons are thus captured in proportion to the charge on the surrounding storage surface and are then accelerated through the aperture to the corresponding phosphor dot in alignment therewith to produce a color presentation.

What is claimed is:

l. A half-tone direct viewing storage tube comprising, in combination, a viewing screen, a storage screen, an electron producing means, a reflector having a continuous channel therein, an electrically continuous filamentary cathode disposed in said channel and adapted to be heated directly, and a plurality of leads extending through said reflector and electrically insulated therefrom, said leads being connected at one end thereof to spaced points along said filamentary cathode and alternate leads connected at the other end thereof to respective common junctions.

2. A half-tone direct viewing storage tube comprising, in combination, a viewing screen, a storage screen, an electron producing means, an annular reflector having a channel therein, an electrically continuous filamentary cathode disposed in said channel and adapted to be heated directly, and a plurality of leads extending through said reflector and electrically insulated therefrom, said leads being connected at one end thereof to spaced points along said filamentary cathode and alternate leads connected at the other end thereof to respective common junctions.

References Cited in the file of this patent UNITED STATES PATENTS 1,852,739 Dijksterhuis Apr. 5, 1932 1,985,915 Chelioti Jan. 1, 1935 2,186,393 Ring Jan. 9, 1940 2,532,339 Schlesinger Dec. 5, 1950 2,659,026 Epstein Nov. 10, 1953 2,728,008 Burnside Dec. 20, 1955 2,748,312 Beintema May 29, 1956 2,754,449 Farnsworth July 10, 1956 2,761,089 Haeff Aug. 28, 1956 2,790,929 Herman Apr. 30, 1957 2,806,174 Pensak Sept. 10, 1957 2,864,020 Rudnick Dec. 9, 1958 

